An example of a known fastener is shown in European Patent Application EP1817240 which describes a fastener comprising a band and a head for holding the band in a closed loop. The band comprises a plurality of teeth on one side of the band. The head comprises passageways for receiving the ends of the band. Each passageway comprises at least one tooth which is arranged to engage the teeth on the ends of the band and prevent the band from being removed from the head.